Environmentally protected housings are used in a wide variety of applications, including containing and protecting electronic components of the type used for transferring signals over long distances. For example, the telecommunications industry transfers signals over optical fibers. If the signal is transferred over a long distance, the signal may be too weak by the time it reaches its destination to be useful. Consequently, electronic circuit cards are used to detect, clean up, and amplify a weak signal for retransmission through another length of fiber-optic cable. These electronic circuit cards are often deployed in environmentally protected housings located above and below ground.
Increased demand on the telecommunications industry to meet the needs of internet subscribers has resulted in the need to transfer more and stronger electrical signals over greater distances. One way of accomplishing this is to amplify the signals using electronic circuit cards deployed in environmentally protected housings. To meet the need for transferring stronger electrical signals over greater distances, electronic circuit cards having higher amplification capabilities and thus greater heat dissipation rates are typically used. The need for stronger electrical signals may be accommodated by placing as many of these higher-heat-dissipating circuit cards into a single environmentally protected enclosure as possible.
As the level of heat dissipation increases, a mechanism for removing this heat from electronic components in an enclosure is required. One simple cooling method is to force outside air through a filter and over the hot surfaces of the electronics, and then exhaust this heated air out into the environment. This cooling method, however, has some inherent design flaws. First, the filter requires regular maintenance and can become clogged quickly in extreme environmental conditions. Second, if the enclosure is placed below ground, water ingress is a concern, therefore, an enclosure that is completely sealed needs to be used.